Suitability of different foamed bitumens for warm mix asphalts with increasing recycling rates

- Different foamed bitumens were studied to be used in warm asphalt mixtures.
- Decay curves of foamed bitumen assessed by a laser device were studied in detail.
- Foam index and suitable foam quality space are key tools for foamed bitumen studies.
- Better foamability was found for soft binders, 3% water content and 0.1% additive.
- Foamed bitumen allows production of durable recycled mixtures at lower temperatures.

Due to the current need for more sustainable production processes and construction materials, foamed bitumen has become one of the most interesting solutions for asphalt paving works, both for new (warm mix) and recycled asphalt mixtures (warm recycled mix). However, significant work still needs to be carried out in order to fully understand the performance of foamed bitumens, and their adequacy for incorporation into asphalt mixtures with different amounts of reclaimed materials, which is the main objective of this work. Three types of bitumen, with increasing penetration grades were selected in order to evaluate their foaming properties, namely their expansion ratio and half-life, as well as the foam index assessed using the foam decay curves obtained through a semi-automated process. After determining the most suitable composition of each foamed bitumen (water content, temperature, foam stabilizing additive content), these were incorporated into asphalt mixtures with 0%, 30% and 50% reclaimed asphalt material. As the amount of reclaimed material increased, the penetration grade of the new bitumen added was also increased, in order to compensate the lost properties of the aged binder. The suitability of these solutions was assessed through water sensitivity tests, and it was concluded that the proposed approach is adequate to obtain long-lasting solutions. Moreover, it became evident that foamed bitumens perform better when incorporated into recycled asphalt mixtures.

186